The research will deal primarily with the perceived intensity of odorous mixtures and with the ability of human subjects to resolve small differences in the concentration of odorants. Experiments on mixtures will address the question of how the intensity of a mixture relates to the perceived intensity of the unmixed components. Attention will be paid to whether mixtures containing malodorants and putative "counteractants" behave any differently from mixtures containing malodorants and substances chosen on the basis of quality, rather than on the basis of their reputation as counteractants. Experiments will also explore mixtures containing a benign odorant and a strong, but relatively odorless, irritant. A primary question of interest will be whether irritation has the ability to mask odor and vice versa. Experiments on intensity resolution will focus on whether normal random fluctuation in the concentration of the odorous stimulus is the limiting factor in intensity resolution. A primary goal in this aspect of the project is to develop the gas-chromatograph as an ideal observer that could be used to predict the performance of the human observer. BIBLIOGRAPHIC REFERENCES: Hall, M. J., Bartoshuk, L. M., Cain, W. S., and Stevens, J. C. PTC taste blindness and the taste of caffeine. Nature, 1975, 253, 442-443. Cain, W.S. Olfaction and the common chemical sense: Some psychophysical contrasts. Sensory Processes, 1976, in press.